Mechanically activated SHS of Nb5Si3 and Nb5Si3/Nb composites

Abstract

Nb5Si3 and Nb are the main components of niobium silicide-based composites, which are promising materials for high-temperature structural applications. Self-propagating high-temperature synthesis (SHS) is an attractive method for fabricating advanced materials from powders via exothermic reactions between the mixture constituents. However, to overcome kinetic difficulties of Nb–Si reaction, SHS of niobium silicides usually requires additional heat input. The present work focuses on a technique that addresses this problem by adding a mechanical activation step before SHS. Specifically, short-term ball milling was used for mechanical activation of Nb/Si mixtures with the goal of conducting SHS of Nb5Si3 and Nb5Si3/Nb composites with no preheating. The milled mixtures were compacted and ignited in an argon environment. It has been shown that a planetary mill is an effective tool for mechanical activation of Nb/Si mixtures. Milling for 10 min enabled SHS of the product that consisted of α-Nb5Si3 and γ-Nb5Si3 phases with traces of Nb3Si. For the first time, Nb5Si3/Nb composites were obtained by mechanically activated SHS with no preheating. Combustion took place at an Nb/Si mole ratio as high as 3, i.e. at 25 at% Si in the mixture. At this mole ratio, a spinning propagation of the combustion wave was observed, and the content of the γ phase, which has poor mechanical properties, was dramatically decreased.